JP4867183B2 - Sand cover structure and sand cover method of bottom soil - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a sand-covering structure and a sand-covering method for bottom-soil covering sandy bottom soil such as sea bottom and lake bottom, in particular, water bottom composed of bottom-soil in a deteriorated environment. .

  Sediment soil that constitutes the bottom of the sea, such as the seabed and lake bottom, changes its state due to various reasons such as the influence of waves and currents, and becomes sludge when the environment deteriorates. That is, in the sea and lake, a lot of organic matter flows from the river, and plankton and seafood grow based on abundant nutrients. Some of these organic matter, and the dead and excrement of the grown organisms are decomposed, but in the seas and lakes where the production of organisms is thriving, most of them sink without being decomposed and deposit on the seabed and lake bottom. In this way, when the accumulation of organic matter on the seabed and lake bottom increases, the sediment becomes so-called sludge. Organic matter deposited on the sea and lake bottoms is gradually decomposed by microorganisms and the like, but consumes oxygen. The decomposition of organic matter by microorganisms becomes more active as the water temperature increases, so that a large amount of oxygen is consumed in the bottom layer during the high water temperature period (summer season). For this reason, when the supply of oxygen from the upper layer cannot catch up, oxygen in the water disappears near the sea bottom and the lake bottom. This is called hypoxia on the sea floor and lake bottom. As described above, the sludge-like sediment contains a lot of organic substances, and oxygen is consumed to decompose them. As a result, living organisms with less oxygen become difficult to live and the biological environment deteriorates. Therefore, conventionally, sand covering is performed in which the upper surface of such sediment is covered with a sand covering material made of a debris material such as sand and covered.

  Conventionally, sand is used as a sand covering material. As sand, mountain sand (mainly crushed stone) is often used. Sea sand (mainly including dredged soil and sea sand) and river sand are also used. These sands are almost the same material as the sediments that make up the bottom of the water, and are almost the same as the sediments that are easily washed away by waves and ocean currents. Therefore, there has been a problem that the sand is washed away with the sediment after covering the sand. Sediment (bottom soil) refers to sediments and basement rocks (if it is the sea, sea sand and seabed soil) that make up the bottom of the water. Note that the sand-capping work is carried out by carrying a sand-capping material (sand) to the surface of the sand-covering position by a ship, and dropping the sand from there to cover the upper surface of the bottom sediment.

  However, as described above, the conventional technology uses natural resources such as mountain sand (crushed stone sand) and sea sand (silent soil) for covering sand, so that there is a problem that nature is destroyed and the environment is deteriorated. In addition, even if sedimentary sand is covered with these sands, the covered sand is easily affected by waves and currents, and since it is washed away after sanding, it is difficult to maintain the state and maintenance is complicated. There's a problem. Moreover, once it is washed away, it is necessary to construct sand-covering sand again, and there is a problem that costs are increased due to repetition. Furthermore, if the sand covered with sand is washed away, there will be another problem that sediments with a poor environment will appear again and adversely affect living organisms.

  In the conventional technology for covering sand using sand, in order to prevent the sand-covering material from being washed away by waves or currents, the sand-covered sand-covering material is surrounded by sand so as to build a bank (such as this) A debris material that builds a bank is called “submarine bank material”, and a sand-clad structure that makes sand-clad material difficult to flow has been devised.

  However, even in such a double sand-covering structure of sand-clad material and submerged dike material, the sand-carrying material and submerged dike material are the same material, and the sand is almost the same quality as the bottom soil. Because of this material, problems caused by waves and currents cannot be solved.

  In addition, in the double structure, an attempt has been made to make the average particle size of the submerged levee material larger than that of the sand-capping material so that the sand-carrying material is not easily washed away. Cannot be resolved.

  Therefore, the object of the present invention is to solve the above-mentioned problems, to be hardly flowed by waves and flows, to improve the biological environment, and to improve the working efficiency, and to provide a sand-covering structure and sand-covering method for sediment. Is to provide.

  In order to achieve the above object, the present invention has the following configuration.

[1] The number of shields covered with sediment on the bottom soil that constitutes the bottom of the water and having the number of shields less than the number of shields of the bottom soil, and the number of shields surrounding the entire periphery of the sand cover material Is a sediment-covering structure of bottom soil composed of a submerged dike material having a number of shields less than the number of shields of the sand-covering material, wherein the sand-covering material is supplied into a hole opened in a water bottom, and the top surface of the sand-covering material is Sedimentary soil characterized in that the submerged levee material is arranged over the entire periphery of the rim, and the sand-clad material is arranged in a ring of the submerged levee material. Sand cover structure.

  [2] The sediment covering structure for sediment according to [1], wherein the sand-clad material is made of granulated slag, and the submerged dam material is made of steel-making slag.

  [3] The sediment covering structure of the sediment according to [1] or [2], wherein the sediment is a sediment with a deteriorated environment.

[4] The bottom soil constituting the bottom of the water is covered with a sand covering material having a number of shields less than the number of shields of the bottom soil, and the entire periphery of the sand covering material has the shields number of A sand covering method for bottom soil, surrounded by a submerged dike material having less than the number of shields of the sand covering material, wherein the sand covering material is supplied into a hole opened in a water bottom, and an edge of an upper surface of the sand covering material A method for covering sand in sediments, characterized in that the submerged dam material is supplied over the entire circumference of the edge, and the sand covering material is arranged in a ring of the submerged dam material. .

[5] The sediment covering method for bottom soil according to the above [4], wherein granulated slag is used as the sand covering material and steel slag is used as the submerged bank material .

[6] The method for sand-covering bottom sediment according to [4] or [5], wherein the sand-covering material is covered on the bottom sediment in a state where the environment is deteriorated .

  (1) The bottom soil is covered with sand-capping material, the periphery of the sand-covering material is surrounded with a submerged dike material, the number of shields of the sand-carrying material is set to be less than the number of shields of the bottom soil, and the submerged dike material By defining the number of shields to be less than the number of shields of the sand covering material, it is possible to obtain a sand covering structure that is excellent in wave resistance stability and is not easily washed away by the ocean current.

  (2) Granulated slag and steelmaking slag are materials excellent in wave resistance stability with a smaller number of shields than bottom soil, and by using granulated slag as sand-capping material and steelmaking slag as submerged levee material Therefore, it is possible to obtain a sand-covered structure that is not easily washed away by waves and ocean currents, and it is possible to stably cover sludged sediments over a long period of time.

  (3) By using granulated slag and steel slag generated in the steel manufacturing process, natural resources such as mountain sand and sea sand do not need to be used, and natural destruction by crushed stones and dredging is not performed, reducing the environmental burden. Is done.

  (4) The slag generated in the steel manufacturing process, that is, the so-called recycled material can be effectively used.

  (5) Granulated slag used as a sand-capping material is a material having a good biocompatibility that has no adverse effects on sediment organisms, and can provide a favorable biological environment.

  Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a cross-sectional view showing a sand covering structure according to a reference example . In FIG. 1, 1 is the water surface of the sea, and 2 is the sediment that forms the bottom of the water. In the present embodiment, a place (hereinafter referred to as “sand covered place”) 2 a that needs to be covered with sand due to deterioration of the environment of the sediment 2 is covered. The place where the environment of the bottom soil has deteriorated is, for example, sludge. The sand covering material 3 is arranged on the upper surface of the sand covering portion 2a. The top surface of the sediment 2 around the sand-capping material 3 is constructed so that the submerged levee material 4 is built around the entire circumference of the sand-capping material 3 and the sand-carrying material 3 is earthed. Yes. In the present embodiment shown in FIG. 1, the cross-sectional shape of the submerged dike material 4 is formed in a truncated triangle. The shape is stable against the flow.

  In the present invention, a debris material having a shields number less than the shields number of the sediment 2 is used as the sand covering material 3, and a debris material having a shields number less than the shields number of the sand covering material 3 is used as the submerged dike material 4. Should. That is, the number of shields of the bottom soil> the number of shields of the sand covering material> the number of shields of the submerged levee material should be satisfied. As will be described later, the Shields number is a value indicating the ease of being swept away by waves or ocean currents.

  In the present embodiment, granulated slag is used as the sand covering material 3, and steelmaking slag is used as the submerged dam material 4. The number of shields of the granulated slag is less than the number of shields of the bottom soil 2, and the number of shields of the steelmaking slag is less than the number of shields of the granulated slag. Therefore, by using the granulated slag as the sand covering material 3, the number of shields of the sand covering material 3 can be made less than the number of shields of the bottom soil 2, and by using the steelmaking slag as the submerged bank material 4, the latent The number of shields of the bank material 4 can be made less than the number of shields of the sand covering material 3.

  Furthermore, by surrounding the sand-clad material 3 made of granulated slag with a submerged dike material 4 made of steel-making slag, the sand-clad material 3 is less likely to be washed away by waves or ocean currents than when the sand-clad material alone is used. Sand portion 2a can be covered with sand stably over a long period of time. Further, the granulated slag is a material having a good biocompatibility that does not adversely affect sediment organisms, and can provide a favorable biological environment to the sand-covering structure portion covered with the sand-covering material 3.

  In order to construct a sand-clad structure as shown in FIG. 1, a sand-clad material 3 and a submerged dam material 4, in this embodiment, granulated slag and steelmaking slag are carried by a ship (not shown), Granulated slag (sand covering material 3) is lowered from the water surface 1 of 2a to cover the upper surface of the sand covering portion 2a, and then from the ship so as to surround the periphery of the sand covering material 3 covering the upper surface of the sand covering portion 2a. The steelmaking slag (submerged dike material 4) is lowered to surround the entire surface of the sand covering material 3 with the submerged dike material 4, and a bank is built around the sand covering material 3. Further, if necessary, the submerged dam material 4 is earthed by work from the ship, and thus the sand covering structure composed of the sand covering material 3 and the submerged dam material 4 is the upper surface of the bottom soil 2 (sand covering portion 2a). Built in.

  Next, the granulated slag and the steelmaking slag will be described.

  As slag generated in the steel manufacturing process, blast furnace slag such as blast furnace slow-cooled slag, blast furnace granulated slag (hereinafter referred to as “granulated slag”), decarburized slag generated in pretreatment, converter, casting process, Steelmaking slag such as dephosphorization slag, desulfurization slag, desiliconization slag, and cast slag, ore reduction slag, electric furnace slag, and the like can be given. In the present embodiment, granulated slag is used as the sand-capping material, and steelmaking slag is used as the submerged dam material. Granulated slag is a granular material obtained by removing iron from the hot metal discharged from the blast furnace and cooling it with water. Steelmaking slag is a granular material generated in the processes of pretreatment, converter, and casting.

  Below, an example of the composition of granulated slag is shown.

Granulated slag _{FeO: 0.3%, CaO: 42.0} %, SiO 2: 33.8%, MnO: 0.3%, MgO: 6.7%, Al 2 O 3: 14.4%.

  Furthermore, an example of the composition of steelmaking slag (decarburization slag, dephosphorization slag, desulfurization slag, desiliconization slag) is shown.

Decarburized slag _{Fe: 17.5%, CaO: 46.2} %, SiO 2: 11.7%, Al 2 O 3: 1.4%, MgO: 8.3%, MnO: 6.2%, P: 0. 76%, S: 0.04%.

Dephosphorization slag Fe: 5.8%, CaO: 54.9%, SiO ₂ : 18.4%, Al ₂ O ₃ : 2.8%, MgO: 2.3%, MnO: 1.9%, P: 2. 8%, S: 0.03%.

Desulfurized slag _{Fe: 10.5%, CaO: 50.3} %, SiO 2: 10.0%, Al 2 O 3: 5.4%, MgO: 1.1%, MnO: 0.4%, P: 0. 13%, S: 1.8%.

Desiliconized slag _{Fe: 10.5%, CaO: 13.6} %, SiO 2: 43.7%, Al 2 O 3: 3.8%, MgO: 0.4%, MnO: 15.8%, P: 0. 10%, S: 0.19%. (End of wt.%)

Moreover, when using for this invention, it is preferable that the median particle size of granulated slag is about 0.5-2 mm, and the median particle size of steel-making slag is more than the median particle size of granulated slag. The median particle size corresponds to the median cumulative value (50%) of the cumulative curve, which is a columnar diagram or curve obtained from the relative frequency, that is, the cumulative frequency, by obtaining the cumulative number of particles equal to or less than each particle size group, that is, the cumulative value. The diameter of the particle, which is called the median diameter or median dia-meter d _med . The number of particles equal to or larger than this size is equal.

  Next, the number of shields will be described.

  (1) The stability index of sediment (bottom soil) includes the force (bottom shear force) to move the sediment due to waves and flows as shown in FIG. 8 and the resistance force (friction) due to the weight of the sediment. Shields number (dimensionless number) represented by a ratio to (resistance) is used.

  The following formula is proposed by T. Shibayama and K. Horikawa for calculating the Shields number ψ.

Calculation of Shields number ^{_{ψ ψ = (1/2) · fu}} b 2 / {(p s / p-1) gd} ··· Equation (1)
here,
f: friction coefficient,
u _b : bottom water particle velocity amplitude,
p _s : Density of sediment particles p: Density of fluid g: Gravitational acceleration d: Particle size of sediment

ここで、
σ：波の角周波数
ｋ_ｓ：粗度高さ（平坦床では底質粒径）
ｖ：動粘性係数 Friction coefficient f

here,
σ: Angular frequency of wave k _s : Roughness height (Sediment particle size on flat floor)
v: Kinematic viscosity coefficient

  (2) An explanation will be given of the calculation of the number of shields by sediment.

(2.1) Sediment material used in the experiment The experiment was based on sea sand (Sagami Bay). For granulated slag and steelmaking slag, in order to eliminate the influence of the particle size, sieving was performed, and the particle size distribution (particle size accumulation curve) of sea sand was adjusted to be approximately the same (average particle size: 1.0 mm). . The density of each is shown in Table 1.

(2.2) Experimental equipment The experiment was performed using a wave-making channel 11 made of double-sided glass with a length of 13.5 m, a width of 0.9 m, and a height of 0.8 m. The wave making channel 11 has a reflected wave absorption type wave making device 6, and can produce regular waves and irregular waves with a period of 0.7 to 2.0 seconds and a wave height of 20 cm. 9 and 10 show the wave making channel.

  In order to conduct experiments on granulated slag 5 and sand 7 at the same time on a part of the horizontal floor at the bottom of this waterway, two soil tanks 8 of length 2.0m x width 0.445m x height 0.1m are placed. In the middle, a dividing wall 9 having a thickness of 10 mm was provided to divide the water channel into two.

(2.3) Implementation conditions Experiments were performed with regular waves. Table 2 shows the experimental conditions. The wave height started from a small wave height where the sediment did not move and gradually increased until the sediment began to move clearly.

(2.4) Experimental method The granulated slag 5 and sand 7 are thrown free from a position 10 cm above the water surface so as to be close to the natural state, and then laid so that they are at the same level as the horizontal floor 10. did. The unit volume weight in water at this time was granulated slag 8.8 (KN / m ³ ) and sand 11.8 (KN / m ³ ). The state of installation of bottom sediment (granulated slag 5, sand 7) is shown in FIG.

  The experiment started with a small wave height and gradually increased the wave height until it was clear that sediment movement was evident. The wave was allowed to act for 5 minutes, the wave height and flow velocity data were measured at a sampling interval of 0.02 (sec), and the state of sediment movement was confirmed by visual observation and video shooting. This time, the movement limit was determined when the entire surface was moved, and the wave height (limit wave height) and the number of Shields (calculated from the bottom surface velocity) when the granulated slag and sand reached the entire movement limit were compared. .

(3) Experimental results (3.1) Comparison of movement limit wave heights The relationship between d / L ₀ and H / L ₀ at the entire movement limit is shown in FIGS. The solid line in the figure is the calculated value obtained from equation (1) for the current experimental conditions, and the plot shows the experimental results of granulated slag (■, ▲, ●) and sand (×) for each condition (cycle) Are shown separately.

  As a result, under the present experimental conditions, the granulated slag and sand movement limit wave heights were the same or slightly larger for the granulated slag. This is thought to be due to the fact that the granulated slag is angular and the friction angle is slightly larger than that of sand. In addition, both the granulated slag and sand have a movement limit wave height (at the total movement limit) that is equal to or greater than the calculated value in equation (2). It turned out to be safe even if used.

(H / H ₀ ) ⁻¹ sinh (2πh _i / L) = α (H ₀ / L ₀ ) (L ₀ / d) ⁿ (2)

(4) Calculation of the number of shields Table 3 shows the number of shields for the bottom sediment when the entire surface movement limit is reached (initial movement before the scavenging movement occurs). Measurement data from the anemometer was used to calculate the number of shields. Table 4 shows the slag values when the number of shields in Table 3 is 1.0 for sea sand. From the above, it can be seen that granulated slag and steelmaking slag, which have a smaller value of the Shields number than sea sand, are less likely to be washed away by waves and ocean currents.

  Next, embodiments of the present invention will be described with reference to the drawings.

Figure 2 is a sectional view showing the "according Kutsugaesuna structure to the actual Example 1 (Reference Example), FIG. 3 is a plan view. Water bottom of sediment soil 2 Kutsugaesuna portion 2a constitutes are inclined Therefore, most of the periphery of the sand-capping material 3 is surrounded by the submerged dam material 4 upward from the lower end of the slope, and the upper end of the slope of the sand-covering material 3 is not surrounded by the submerged dam material 4. Since the sediment 2 is inclined, the sand-capping material 3 is not washed away by waves or ocean currents even if configured in this way.

Figure 4 is a sectional view showing a Kutsugaesuna structure according to actual施例2 (Reference Example). As shown in FIG. 4, this is a case where a large hole is opened in the bottom of the water. Such holes can be artificial or natural. The sand covering material 3 is supplied more than the height of the edge of the hole, and the periphery of the sand covering material 3 is surrounded by the submerged dike material 4 arranged on the upper surface of the sediment 2 outside the hole.

Figure 5 is a sectional view showing a Kutsugaesuna structure according to actual施例3 (Reference Example). In FIG. 5, the sand covering material 3 is surrounded by the submerged dam material 4 supplied to the inner periphery of the hole and the upper surface of the sediment 2 outside the hole.

FIG. 6: is sectional drawing which shows the sand covering structure which concerns on Example 4 (invention example) of this invention . In FIG. 6, the sand-capping material 3 is supplied into the hole, and then the latent dam material 4 is supplied so as to surround the upper surface of the sand-covering material 3, that is, surrounding the hole. The sand covering material 3 is supplied into the ring 4.

Figure 7 is a sectional view showing a Kutsugaesuna structure according to actual施例5 (Reference Example). In FIG. 7, although it is the structure substantially the same as the reference example shown in FIG. 1, in this Example, the cross-sectional shape of the submerged dam material 4 is a rhombus. In the case of FIG. 7, the submerged dam material 4 is placed so that the sand-covering material 3 is placed on top and the end of the sand-covering material 3 is covered, and this shape is obtained.

It is sectional drawing which shows the sand covering structure which concerns on a reference example . It is a sectional view showing a Kutsugaesuna structure according to the actual Example 1 (Reference Example). Is a plan view showing a Kutsugaesuna structure according to the actual Example 1 (Reference Example). It is a sectional view showing a Kutsugaesuna structure according to actual施例2 (Reference Example). It is a sectional view showing a Kutsugaesuna structure according to actual施例3 (Reference Example). It is sectional drawing which shows the sand covering structure which concerns on Example 4 (invention example) of this invention . It is a sectional view showing a Kutsugaesuna structure according to actual施例5 (Reference Example). It is a schematic diagram of the force which acts on sediment. It is a top view which shows an experimental water channel. It is side surface sectional drawing which shows an experimental water channel. It is a perspective view which shows the installation condition of bottom sediment. Is a graph showing the relationship between _{d / L 0, H / L} 0 in the entire surface movement limit state. Is a graph showing the relationship between _{d / L 0, H / L} 0 in the entire surface movement limit state.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Water surface 2 Sediment soil 2a Sand cover part of the bottom which needs sand covering 3 Sand covering material 4 Submarine material 5 Granulated slag 6 Wave making device 7 Sand 8 Earth tank 9 Dividing wall 10 Horizontal floor 11 Wave making channel

Claims (6)

A sand-covering material with a shields number less than that of the bottom soil, which is covered on the bottom soil constituting the water bottom, and surrounds the entire periphery of the sand-covering material. A sand- covered structure of sedimentary soil composed of submarine material with less than the number of shields of sand material , wherein the sand-covering material is supplied into a hole opened in the water bottom, and on an upper edge of the sand-covering material In addition, the submerged soil covering sand is characterized in that the submerged dam material is disposed over the entire circumference of the edge portion, and the sand covering material is disposed in a ring of the submerged levee material. Construction. The sand capping material is water granulated slag, the latent bank material is characterized in that it consists of steel slag, as claimed in claim 1, wherein, Kutsugaesuna structure of the bottom soil. Said bottom soil, characterized in that a sediment soil conditions the environment is deteriorated, according to claim 1 or 2, Kutsugaesuna structure of the bottom soil. The bottom soil constituting the water bottom is covered with a sand covering material having a number of shields less than that of the bottom soil, and the entire periphery of the sand covering material is covered with the sand covering material. It is a sand-covering method for bottom soil, surrounded by a submerged dike material with less than the number of Shields , wherein the sand-covering material is supplied into a hole opened in the water bottom, and on the edge of the upper surface of the sand-covering material, A method of sand-covering sediments, comprising supplying the submerged dam material over the entire circumference of the edge and further arranging the sand-covering material in a ring of the submerged dam material . The method for sand-covering sediments according to claim 4, wherein granulated slag is used as the sand-capping material, and steel slag is used as the submerged dam material . The method for sand-covering bottom sediment according to claim 4 or 5, wherein the sand-covering material is covered on the bottom sediment in a state where the environment is deteriorated .

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